Following up on comments above by Ken and Richard: No, the "short major" overcall of a minor-suit opening bid is not at all something new under the sun. Ken says he toyed with the idea fifteen or twenty years ago, and I don't doubt that he did. In fact, there was an article by Jim Wood in The Bridge World in 1983 entitled "The Anticipatory Overcall," which described exactly this proposed tactic against minor-suit opening bids by people who didn't open five-card majors. (This was before "Could be Short" achieved much of a following, so the minor-suit opening bids in question implied three or more in the suit.) Anticipatory Overcalls were barred by ACBL regulators, who ruled that they were forbidden as controlled psyches. As Richard suggests, life may have been breathed back into that type of defensive method when the minor-suit opening bid (or the one-diamond response) could be on a doubleton (or less) and as such is conventional, as it appears that they might be in the version of Montreal Relay that Ken describes. It might be fun when opponents announce minor-suit opening bids that could be short to respond that we are playing "Could be Short vs. Could be Short," meaning that our major-suit overcalls could also be on a doubleton. At least one World Champion pair, Bocchi-Duboin, have advertised that they were playing "canape overcalls" over standard minor-suit opening bids. By this they meant the 1M overcall would be on two or three cards, with a 5+-card suit somewhere else in the hand. I don't think they played that 1M might also be just a normal long-suit overcall. (Woods' Anticipatory Overcall could be either short or long.) I don't know what kind of results they had with canape overcalls, and I don't know whether anyone is still playing them.